Journal of Nannoplankton Research, 22, 3, 2000.

H. Okada: An improved filtering technique ... , p. 203-204.

AN IMPROVED FILTERING TECHNIQUE FOR CALCULATIONOF CALCAREOUS NANNOFOSSIL ACCUMULATION RATES
Hisatake Okada
Division of Earth & Planetary Sciences, Graduate School of Science, Hokkaido University, NJO W8, Sapporo 0600810, Japan; oka@ep.sci.hokudai.ac.jp

sample before drying, but grinding is strongly prohibited.
Introduction
2. A portion ofsampleweighingbetween 0.01 and 0.02g
Numerical abundances of microfossils in sediment areroutinely calculated for most of the major microfossil
is weighed, with an accuracy of0.0001g.
3. The weighed sample is placed in a graded 20ml testgroups. Because of their very small size and numericallyastronomical populations , however, the absolute . tube and 1Oml ofbuffered distilled water is added. Ordinalabundances of nannofossils per unit of sediment (# piston core samples or crushed rock samples do not requirecoccolith/g) have long been substituted for by simple chemical additives but, if necessary, organic matter can beadjectives for relative abundance, such as abundant, removed using 5-10% hydrogen peroxide or clay can becommon, few/frequent and rare. Modern palaeocea- deflocculated using 0.5N sodium metaphosphate (or anography utilises various proxies, and the numerical detergent) (Mclntyre et al., 1967). In any case, make theabundance of nannofo'ssils can be an useful tool for volume of sample suspension up to lOml. Ifyou use any
palaeoceanographic analysis.
chemical additives, the sample should be left for several
Over the last 10 years, various techniques have been hours.
4. Agitate the sample suspension ultrasonically for 10
proposed to calculate the numerical abundance of
seconds and homogenise it by pressing the tube against
nannofossils, and these can be class.ified into four groups:
1) smear-slide method; 2) microbeads method; 3) settling the swivel-head of a tube-mixer (or touch -mixer) for several
method; and 4) filtering method. Baumann et al. (1999)
seconds. Immediately following homogenisation, a fraction
presented an excellent review and evaluation of these of sample suspension is extracted with a micropipettetechniques. The widely-used smear-slide method gives (between 50 to 10001J.l, depending upon the richness ofnannofossils) and poured into a small beaker containing
only semiquantitative data, and it requires some training to
make good slide. Okada (1992) proposed the use of 150 to 200ml ofbuffered distilled water.
5. The contents of the beaker are mixed with a stirring
microbeads for calculation of relative abundances ofrod and filtered through a plain white, 47mm diameter,nannofossils, and Bollmann et al. (1999) invented anelaborated spraying technique with microbead spiking 0.451J.ffi pore-size, type HA Millipore filter. The filter is dried(SMS method) to calculate the numerical abundance. The in a drying oven at a temperature of about 50°C. Drying
SMS method seems to be a rapid and reliable technique, will be completed within 10 to 30 minutes.
6. An approximately 1.2cm x 1.2cm portion ofthe dried
but may be a bit too cumbersome for some workers.
Although it requires no special equipment, the settling filter is cut out and placed on a glass slide. The piece ofmethod (Beaufort, 1991; Flares & Sierro, 1997; Geisen et filter is rendered transparent with a drop of immersion oilal., 1999) requires a working-spacethatmustbeundisturbed and covered with an 18mm x 18mm coverslip. The fourfor 12 to 24 hours, and also carries a possibility of corners of the coverslip are fixed to the slide using nailassemblage alteration (Baumann et al. , 1999; Bollmann et polish.
7. The slide is examined under a polarising lightal. , 1999). The filtering technique proposed by Andruleit
microscope at x640 to x1250 magnification, and the total(1996) requires shorter preparation time and cause lessassemblage alteration but uses a rotary splitter that is rather number of nannofossils observed within a known view
expensive and is not a tool ordinary laboratories are usually field is recorded.
The amount of sediment on the filter ranges between
equipped with.
I have attempted to improve on Andruleit's (1996) 0.005mg and 2.0mg. Depending upon the filtering device
filtering technique by using inexpensive and commonly employed, the filtered area may vary, but it normallyavailable laboratory apparatus. As an additional advantage measures around 1000mm2• By measuring the proportionsof the observed area, the counted nannofossil number canofthe new technique, it uses less glassware (less washing)
and requires a smaller working-space. In addition to the be converted to numerical abundance per gram of sediment.
abundance study, the slide prepared by this new method Numerical abundances ranging between several thousands
to tens of billions (n x 103/g ton x 10 10/g) can be measured
can be used for the investigation of species assemblages
by this technique.
with a light-microscope or an SEM.
The nannofossils soaked in the immersion oil tend tobecome
etched or dissolved after several months ofMethodology
The new technique proposed here can be summarised as storage. The speed of corrosion varies between different
brands, and Zeiss's own brand seems to be the least
follows:
harmful (J. Young, pers. comm., 2000). But even the Zeiss
1. A small amount of sediment sample is dried in a drying
oven at a temperature of about 50°C. For indurated samples, oil causes significant dissolution after several months ofa mortar and pestle should be used to gently crush the storage. ·It is, therefore, advised that light-microscopea203

Journal of Nannoplankton Research, 22, 3, 2000.

H. Okada: An improved filtering technique... , p. 203-204.

observation should be completed within one month of theslide-making. The filter itself can be stored safely for manyyears, and you can remake the microscope slide ·whenevernecessary. According to my experience, there are nosuitable optical (photo-curing) adhesives available to beused for permanent mounting of the Millipore filter; someare too viscous to penetrate the filter fabric, and others
make the filter cloudy after UV treatment.
Acknowledgement
I am much obliged to Jeremy Young for the valuable
information and comments.

References
Andruleit, A.H.1996. A filtration technique for quantitative
studies of coccoliths. Micropaleontology, 42(4): 403-406.
Baumann, K.-H., Andruleit, A.H. & Xin, S. 1999. Comparisonof different preparation techniques for quantitative

nannofossil studies. Journal of Nannoplankton Research,20(2): 75-80.
Beaufort, L. 1991. Adaptation of the random settling method forquantitative studies of calcareous nannofossils .
MiC!vpaleontology, 37:415-418.
Bollmann, J. , Brabec, B., Cortez, M.Y. & Geisen, M. 1999.
Determination of absolute coccolith abundances in deepsea sediments by spiking with microbeads and spraying(SMS method). Mar. Micropaleontol., 38(1): 29-38.
Flares, J.A. & Sierra, F.J. 1997. Revised technique for calculationof calcareous nannofossil accumulation rates.
Micropaleontology, 43(3): 321-324.
Geisen M., Bollmann J., Herrle J.O., Mutterlose, J. & Young,J.R. 1999. Calibration of the random settling technique forcalculation of absolute abundances of calcareous
nannoplankton. Micropaleontology, 45(4): 437-442 .
Mclntyre, A., Be, A.W.H. & Preikstas, R. 1967. Coccoliths andthe Pliocene-Pleistocene Boundary .. Progress inOceanography, 4: 3-27.
Okada, H . 1992. Use of microbeads to estimate the absoluteabundance ofnannofossils. INA Newsletter, 14(3): 96-97.

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